(i) Technical Field
The present invention relates to focal plane shutters and optical apparatus.
(ii) Related Art
A focal plane shutter includes: an electromagnet; a board including an opening; blades capable of opening and closing the opening; and a drive member driving the blades. The drive member holds an iron piece with which the electromagnet is adsorbed, and is movable such that the iron piece moves toward and away from the electromagnet, and is biased by a drive spring such that the iron piece moves away from the electromagnet. Such a focal plane shutter is disclosed in Japanese Unexamined Patent Application Publication No. 9-133944.
High speed of the blades has been demanded in a recent focal plane shutter. When the spring force of the drive spring is increased by increasing of the speed of the blades, the electromagnet might be attracted by the drive spring to be unstable, in cases where the electromagnet is secured by elastic engagement. When the electromagnet is positionally unstable, there may be variations in the position of the iron piece at the time when the iron piece moves away from the electromagnet. This might result in variations in the speed of the blades.